Optimal design of linear subsynchronous damping controllers for stabilising torsional interactions under all possible operating conditions

Torsional damping controllers, such as supplementary excitation damping controllers (SEDCs), are widely used to stabilise subsynchronous resonance (SSR) induced by torsional interactions (TIs) between turbo-generators and series-compensated power systems. However, because of the changeable operating situations of a power system, it is a great challenge to design them to guarantee torsional stability under all possible operating conditions. This study proposes a global optimal control-design procedure for tuning SEDCs to accommodate the variation of system conditions. Considering TI is a small-signal stability issue, the non-linear power system is converted into a family of linear parameter varying models and the parameter-tuning task for multiple SEDCs is formulated into a multi-model constrained non-linear optimisation problem. A global optimisation procedure based on genetic algorithm and simulated annealing is designed to efficiently solve this problem and obtain a set of robust or several sets of gain-scheduling SEDCs. The proposed method is applied to a multi-machine series-compensated power system. The results of both eigenvalue analysis and time-domain simulation have fully demonstrated the effectiveness of the optimised SEDCs in stabilising SSR under all possible operating conditions.